The present invention relates to a catalytic converter for use in an exhaust system of an automotive internal combustion engine and more particularly to a catalytic converter of the type having a metallic casing with a monolithic catalytic element securely but resiliently mounted within the casing by a resilient flexible intumescent sheet having generally sinusoidal edges such that mounting pressure is applied to the lateral surface of the ceramic monolith in the area circumscribed by the generally sinusoidal edges.
Catalytic converters are universally employed for oxidation of carbon monoxide and hydrocarbon and reduction of the oxides of nitrogen in automobile exhaust gases in order to control atmospheric pollution. Due to the relatively high temperatures encountered in these catalytic processes, ceramic has been the natural choice for catalyst supports. Particularly useful supports are provided by ceramic honeycomb structures as described, for example, in U.S. Pat. RE No. 27,747.
Ceramic bodies tend to be frangible and to have coefficients of thermal expansion differing markedly from the metal, usually stainless steel, containers. Thus, the mounting means of the ceramic body in the container must provide resistance to mechanical shock due to impact and vibration and to thermal shock due to thermal cycling. Both thermal and mechanical shock may cause deterioration of the ceramic support which, once started, quickly accelerates and ultimately renders the device useless. Intumescent sheets that have been found useful as mounting materials for this purposes are disclosed in U.S. Pat. Nos. 3,916,057 4,305,992, and U.K. Pat. No. 1,513,808.
It has been found that the above intumescent sheet materials may exert substantial pressures on the ceramic monoliths of catalytic converters. These pressures, combined with the shear modulus, the coefficient of friction and the coefficient of thermal expansion of the intumescent sheet material and the axial thermal expansion of the container may cause cracks within the ceramic monolith. These cracks are termed "ring off" cracks and occur perpendicularly to the gas flow usually near the center of the monolith. In severe cases, the ceramic monolith is completely severed into two pieces.